what is the difference between SDHC & SDXC

does anyone work with SDXC memory card?
in 2013 i made a seismostation which writes data on SDHC card with 32 Gb capacity
now i need to write more then 32 Gb data
and i try to use SDXC for that
i read specs and i don't find difference in initialization both types of cards
may be i haven't paid attention to something ?
is there a difference in power connection between SDHC and SDXC
or initialization sequence ?